SharePoint power automate, read image content from InfoPath base64 string

Question

Update:

After research I found that unfortunately it is impossible for now (April 2023) to work (to cut/split) binary data with PowerAutomate functions. Here is same problem described: https://poszytek.eu/en/microsoft-en/office-365-en/powerautomate-en/how-to-move-copy-infopath-attachments-in-sharepoint-online/

Autor Tomasz Poszytek used Azure function and premium connector. Tried to find free solution but seems there is no such.

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Infopath XML stores embedded images in base64 string, which contains file name/type and file content. Here are two embedded images:

In Infopath XML this image is stored like base64 string:

<my:group4>
    <my:field18>
        <!-- jpg-image.jpg encoded in infopath form: -->
        x0lGQRQAAAABAAAAAAAAAO+aAAAOAAAAcABuAGcALQBpAG0AYQBnAGUALgB...
    </my:field18>
</my:group4>

First part contains file name and the second is encoded image. But we need to encode this data to binary and then split file name/image type and image content itself:

We can then use encoded image <data> part as <img> content like this: 

<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABkAA..." />

But xml string in Infopath stores both filename and content in one line, so I need to convert it to bytes, and then read data byte-per-byte and split file name and image content.

Here I put examples of InfoPath string and C# code, that decodes it and get file name/and content strings:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml;
using System.Xml.XPath;
using System.Security.Cryptography;
using System.IO;


namespace getFilenameFromBase64
{
    class Program
    {

        // "jpg-image.jpg" file encoded in infopath xml
        private static string base64FromInfopath = "x0lGQRQAAAABAAAAAAAAAPBgAAAOAAAAa....";

        // "png-image.png"
        //private static string base64FromInfopath = "x0lGQRQAAAABAAAAAAAAAO+aAAAOAAAAc...";

        static void Main(string[] args)
        {
            // This function from Quazi Anis gets filename from encoded string
            // https://www.infopathdev.com/forums/p/15120/53720.aspx#53720
            Encoding _encoding = Encoding.Unicode;

            // Read base64 string and get header, filename and image content separately
            using (MemoryStream _memoryStream = new MemoryStream(Convert.FromBase64String(Program.base64FromInfopath)))
            {
                BinaryReader _theReader = new BinaryReader(_memoryStream);
                byte[] _headerData = _theReader.ReadBytes(16);
                int _fileSize = (int)_theReader.ReadUInt32();

                int _imageNameLength = (int)_theReader.ReadUInt32() * 2;
                byte[] _fileNameBytes = _theReader.ReadBytes(_imageNameLength);

                // here is file name decoded:
                string fileName = _encoding.GetString(_fileNameBytes, 0, _imageNameLength - 2);
                Console.WriteLine(fileName);                                                // result: "jpg-image.jpg"

                // and here is base64 data of pure image that we can use in html: <img src="data&colon;image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAqMAAAIZCAIAAAAdrK.." />
                var imageContentInBytes = _theReader.ReadBytes(_fileSize);
                var imageContentAsString = Convert.ToBase64String(imageContentInBytes);     // result: "iVBORw0KGgoAAAANSUhEUgAAAqMAAAIZCAIAAAAdrK.."

                Console.WriteLine(imageContentAsString);
            }
        }
    }
}

Here are project sources if needed:

https://github.com/Gennady-G/ExtractImageFromInfopathXml/blob/main/getFilenameFromBase64/getFilenameFromBase64/Program.cs

Can I do something similar (make operations with bytes array) in SharePoint power automate? Or what You think I can do to decode Infopath base64 string and extract file name/type and image content from there?

I attached some InfoPath strings example here in github gists: https://gist.github.com/Gennady-G/48d740c92593e1ce8234b4a8c3a23069

Have no problem to read them from XML, but don't know how to decode and split file name and data

Answer 1

Power Platform has some base64 functions to en/de-code strings and binaries that should do the trick:

#1 https://learn.microsoft.com/en-us/azure/logic-apps/workflow-definition-language-functions-reference#b

Of course you will have to split the string or just get rid of the prefix if it is always the same ("data:image/png;base64,") and maybe save the file (image) in an accessible location (onedrive, blob storage, SharePoint folder, etc)

#2 Another way that worked is in the following picture (better than 10^3 words)